Various mechanisms have been devised for transferring sections of drill pipe between a supply of such pipe and the main drill mast for either installing the pipe sections in the drill oil or for pulling the sections from the well. These prior pipe transfer devices move the pipe from its normal horizontal stored position adjacent the base of the main drill mast or derrick to a vertical position for installation in the drill hole by the equipment mounted on the main mast. Examples of such prior transfer masts and associated equipment are shown in U.S. Pat. Nos. 3,177,944; 3,613,905; 3,633,771; 3,702,640; 4,109,800; and 4,172,684.
Although these prior constructions may perform satisfactorily, they are relatively expensive and difficult to operate and provide a safety problem in that movement of the supply mast or pipe transfer device toward the main drill mast, a workman in the vicinity between the main mast and pipe supply apparatus could be crushed.
A further problem with known pipe transfer devices is the inability of the device to accommodate pipes of various size diameters. Although certain transfer devices have adjustable clamps, the centerline of the pipe with respect to the transfer mechanism will vary depending upon the size of the pipe. This presents alignment problems when the pipe is raised to a pipe installation position with the main mast due to the relocation of the supply pipe centerline. A still further problem with known pipe clamps is that the clamping pressure can damage the pipes secured thereby where relatively thin-walled pipe is used for a particular well installation is contrast to other installations using a heavy-walled pipe. Heretofore the clamps will maintain a constant clamping force regardless of the size and wall thickness of the pipe being clamped thereby.
A further problem with known drilling mast assemblies is that the pipe sections may require manual movement and relocation for placing the pipe sections on the transfer mechanism, all of which increases the number of men required at a drill site as well as the amount of time for loading or unloading the transfer mechanism with a pipe section. Furthermore, this manual handling of the pipe increases the safety risk for the workmen.
Another problem with prior drill assemblies having pipe transfer devices is that the pipe sections are stored on the drilling platform or in the main drilling mast increasing the danger to the workmen and possible damage to the equipment, especially when high winds are encountered due to the excess weight at an elevated position and resulting moment force that is applied to the base of the drilling mast. Therefore, there is the need for an improved drilling mast assembly and pipe transfer mechanism which eliminates these problems which have existed in the art.